Thermotreating method and apparatus



April 27, 1965 c. c. ANTHES EI'AL 3,180,397

THERMOTREATING METHOD AND APPARATUS Filed May 29, 1963 6 Sheets-Sheet li\\\\\ \x \i\\\ I 42 28 30 i2 i2 13 Q; 1 Q 1a IN VE N TORS CLIFFORD C.ANTHES JOHN VlLLORE-Sl M% ATTORNEY WILLIAM C. POLAND,JR.

P" 1965 c. c. ANTHES ETAL THERMOTREATING METHOD AND APPARATUS Filed May29, 1965 6 Sheets-Sheet 2 INVENTORS CLIFFORD C. ANTHES JOHN VILLORESIWILLIAM c. POL'A'ND,JR.

A 7' TORNE Y April 1965 c. c. ANTHES ETAL THERMOTREATING METHOD ANDAPPARATUS 6 Sheets-$heet 3 Filed May 29, 1963 SGNODI-IS NI BWLL .LHVlSLVBHHHd INVENTORS CLIFFORD C. ANTHES JOHN VILLORESI WILLIAM C.POLAND,JR.

ATTOR Y Aprxl 27, 1965 c. c. ANTHES ETAL THERMOIREATING METHOD ANDAPPARATUS 6 Sheets-Sheet 4 Filed May 29, 1963 SGNODBS NI BWLL .LHVJS.LVEIHHUd INVENTORS CLIFFORD c. 'ANTHES JOHN VILLORESI WILLIAM c.POLAND,JP lax WW ATTORNEY April 1965 ch c. ANTHES ETAL THERMOTREATINGMETHOD AND APPARATUS 6 Sheets-Sheet 5 Filed May 29, 1963 in Qw Qv Nv QwlNl/ENTORS CLIFFORD C. ANTHES JOHN VILLORESI WILLIAM c. POLAND,JR. MM%%M,

A TTORNEV United States Patent 3,180,397 THERMOTREATING METHQD ANDAPPARATUS Clifford C. Anthes, Union, John Viiioresi, Lincoln Paris, andWilliam C. Poland, Jr., Irvington, N.J., assignors to Union CarbideCorporation, a corporation of New York Fiied May 29, 1963, Ser. No.289,156 7 Claims. (Ci. 15827.4)

The present invention relates to a blowpipe nozzle or tip for producinga highly efficient heating flame. It relates, more particularly, to amethod and apparatus for utilizing a supersonic heating flame inconjunction with metal-treating operations.

For instance, among the various thermo-treating processes contemplatedby the present invention, are: metal piercing, cutting, welding, flamehardening, or any of the commercially known methods.

Up to the present time, the most widely-used method of applying heat toa workpiece by means of oxy-fuel gas flames has been limited to the useof flames having relatively low gas velocities, and low ratios of oxygento fuel gas. In the following description, we use the term velocity inaccordance with the accepted practice of measuring flow by the formulawhere v is in feet per second, Q denotes quantity of gas in cubic feetper second, and A is the cross-sectional area in square feet of the portthrough which the measured fluid passes.

Generally, the typical oxy-acetylene preheat flame, commonly referred toas a neutral flame, has a maximum ratio (by volume) of oxygen toacetylene of approximately 1 to 1. For fuel gases other than acetylene,the ratios commonly used may vary from 1.3 to 1 to 1.7 to 1 for naturalgas, and 3.5 to 1, to 4, to l for propane. The velocity of the mixedgases leaving the nozzle flame ports generally ranges between 350 and550 ft. per second. Such low exit velocities are considered essential inorder to maintain the low-ratio gas flames on the flame-ports, that is,to avoid their being blown off, a phenomenon usually associated withhigher velocities.

These low-velocity, low-ratio preheat flames are in accordance with themost popularly accepted theory of providing effective preheat. Thistheory is based on the concept that the greater the volume of preheatgases used, the shorter will be the preheat time required to raise ametal workpiece to its ignition temperature. In other words, morepreheat gas is supplied and the size of the preheat flame ports isincreased. Little, if any, consideration is given to what has been foundto be a far more important factor in achieving effective preheat,namely, the combination of the gas-exit velocity and the ratio of oxygento fuel gas.

The result of the wide application of this popularly accepted theory,particularly in the case of oxy-fuel gas cutting operations using theconventional low-velocity, lov-ratio preheat flames, is that the preheattimes generally required are relatively high. For instance, in order tostart a cutting reaction in a steel plate at room temperature, it isusually necessary to raise the temperature of the metal to its sweattemperature, approximately 1808 F. Using the aforementionedlow-velocity, lowratio preheat flames, the preheat time required tobring a steel plate, in. thick or over, to its sweat temperature variesbetween 15 seconds and 1 /2 minutes for pierce start, i.e., when the cutis started by piercing a hole in the interior of the plates. For edgestarts, 5 to 20 seconds is usually required depending upon the actualvelocity, ratio, and volume of gases used.

To consider the economic aspects of metal cutting, for

many years, during which the cost of materials was the primary economicfactor, preheat times ranging as high as 1 minutes were accepted in thetrade. However, with the rising cost of labor making man hours theallimportant factor in cost analysis, such lengthy preheat times havebecome extremely undesirable. For example, in mechanized operations thelargest percentage of metal cuts are initiated by the pierce startmethod which requires the longest preheat time. Combining thismechanized operation with a cutting application on which a multiplicityof short-length cuts are to made, will result in the preheat timebecoming a large percentage of the overall cutting time per out, suchthat the preheat time will become a large-cost factor in the operation.

Recent experimental work has led to a clearer understanding of theimportance of preheat gas-exit velocity, and the ratio of oxygen to fuelgas, to achieve a more effective heating flame. It has been found thatone way of increasing preheat flame effectiveness is to increase theratio of oxygen to fuel gas in the flame above the neutral or molarratio thereby increasing the flame temperature. This also permits usingsomewhat higher gasexit velocities, which is seen to increase theheat-transfer rate. -lowever, full utilization of the benefits to be drived from higher velocity flames normally requies the use of flameholders, such as low-velocity pilot flames or skirted nozzles, whichmaintain the preheat flames on the flame ports. By utilizing suchfeatures, exit velocites as high as 1000 fps. can be attained. However,these velocities so far have been limited to use with fuel gases otherthan acetylene due to the high fuel gas pressures required in order toachieve such velocities with the torch and nozzle apparatus commerciallyavailable. For the same reasons, the requirement for high fuel gaspressures has eliminated the possibility of using these higher gasexitvelocities with low-pressure fuel gases, i.e.: fuel gas supplied fromlow-pressure gas lines of about /2 psi. or less.

A further disadvantage of the above procedures resides in the auxiliaryequipment required to achieve such velocities. The use of low-velocitypilot flames to maintain the main heating flames on the torch nozzlegenerally necessitates either incurring the added expense andcomplications inherent in the use of two separate gas systems to supplythe required fuel gas and oxygen for the two sets of flames, or theinclusion of gas restricting passages leading to the pilot flame ports.The usefulness of the skirted type nozzle to maintain high-velocityflames on the nozzle ports is limited by the fact that the effectivenessof the shirt in retaining the flames is a function of its depth. A skirtwhich is sufficiently deep to be really effective in retaining thehigher velocity flames is soon destroyed by these flames.

It may be readily seen, then, that prior to the present invention it hasbeen virtually impossible to take full advantage of the possibility ofimproving the preheat flame by the use of high-velocity and high-ratiogas mixtures. In the case of acetylene and the low-pressure fuel gases,it has been impossible to use them at all.

It is therefore an object of the invention to provide a more effectiveheating flame exhibiting a higher degree of heat transfer from flame toworkpiece. It is a further object to provide an improved method forpreheating a metal surface prior to initiating a cutting operationthereon. Another object is to provide an apparatus for facilitating suchoperation by directing a flow of preheating gas at supersonic velocitiestoward the metal surface. A still further object is to provide anapparatus for delivering a flow of preheat gas comprising a mixture offuel gas and oxygen at supersonic speeds toward a metal surface, eventhough the fuel gas is supplied from a low-pressure source. Ashereinafter used, the term supersonic or super-sonic flames, refers tothe exit velocity of preheat gases measured by the previously noted Q/Avalue in excess of sonic velocities.

In the figures:

FIG. 1 is a longitudinal view in cross-section through a blowpipenozzle;

FIG. 2 is an enlarged fragmentary view in cross-section of the nozzledischarge portion;

FIG. 3 is an end view taken along line 3-3 of FIG. 2;

FIGS. 4 through 8 are graphical representations of the results obtainedutilizing the disclosed process in metalcutting operations.

In brief, one embodiment of the apparatus of the invention contemplatesan elongated blowpipe tip or nozzle having a central axial passage forcutting oxygen, and an annular, longitudinal passage for conducting apreheat gas mixture toward the nozzle discharge orifice. The inlet endof the nozzle is provided with a customary suitable cohfiguration ofsurfaces for gas-tightedly engaging corresponding surfaces in the headof a blowpipe; the nozzle discharge end is provided with an outlet portfor the cutting oxygen, and preheat gas ports substantially sur-'rounding the outlet port. Each of the preheat gas ports at the nozzledischarge consists essentially of a constricted, gas-metering inlet,preceded by a tapered passage for funneling gas thereto, and a forwardflame port passage of gradually increasing cross-sectional area inproportion to the downstream distance from the metering inlet.

In accordance with the invention and referring to FIGS. 1 and 2, theembodiment of blowpipe cutting nozzle illustrated consists of an innermember or core 12 and an outer jacket 14 substantially surrounding andspaced from the inner member to define an annular chamber 16therebetween. The gas inlet end of the inner member is provided withsuitable seating means such as frusto-conical surface 18 which may bebrought into gas-tight relationship with the blowpipe head to provide aflow of cutting oxygen to the central passage 20. Oxygen from thiscentral passage is normally directed onto a metal surface which has beensufliciently preheated for cutting or metal removal purposes.

A second frusto-conical surface 22 substantially concentric with saidfirst frusto-conical surface, likewise engages the blowpipe head to forma gas-tight seal for preheat gases. This gas mixture, according topractice, may consist of a fuel gas such as acetylene, propane, ornatural gas, and a combustion-supporting gas such as oxygen. A pluralityof bores or passages 24 provide means for conducting preheat gas fromthe blowpipe head to the annular chamber 16. These passages may form aring about the central oxygen passage and are preferably equi-spaced topromote uniformity of flow of preheat gas into said chamber.

The jacket 14 comprises an elongated cylindrical member having a centralbore 23 which tapers toward the nozzle discharge end, and terminates ina short cylindrical opening 23. The short cylindrical opening 28, whichis often termed a skirt is not required when the fuel gas used isacetylene, and in such case, the nozzle front face would be formed flushwith respect to the forward face of core 12. Thus, the jacket 14 wouldnot extend forwardly beyond the forward end of core 12, as shown inFIGS. 1 and 2. The jacket member 14 is disposed substantially concentricwith and surrounding the inner member 12; when properly assembled, thejacket 14 bears rearwardly against a peripheral shoulder 26 on saidmember 12, forming a gas-tight connection to axially position therespective members in the blowpipe head. Conventional fastening meanssuch as a ring nut, not shown in' the figures, may be employed to retainthe two-piece nozzle with sufiicient firmness in the blowpipe head toassure proper passage of oxygen and the preheat mixture without leakage.The forward ends of the respective inner and outer members are so formedas to be in sliding contact when properly aligned. Referring to FIG. 1and enlarged FIG. 2, the central bore 23 of jacket 14, substantiallyconforms in shape to the profile of the core 12 to define the annularpassage 1s. The downstream end of said bore 23 terminates in thecylindrical forward opening 28 which cooperates with andcircumferentially positions the forward portion of the .core 12.Immediately to the rear of opening 28, the central bore sharplyincreases in diameter to define the shoulder approach 38 to the flameports which extend therefrom, to the nozzle face and which will beherein described with particularity. This approach is preferably formedwith an included angle of about 120 to inwardly direct gas toward thecore member and to reduce resistance or pressure drop along the approachto said ports.

The overall nozzle, as above described, represents a generalconstruction rather conventional in the art of cutting nozzles. Theparticular feature of the present invention by which it derives itsutility resides in the unique discharge portion of the nozzle and moreespecially in the configuration of the preheat gas ports 30.

As previously mentioned, one method for achieving a faster preheating ofa metal to be cut, is to deliver a greater quantity of gas to thecutting area and thereby provide a greater number of effective heatingunits. This could be accomplished, of course, by providing asufiiciently large discharge port or ports, and/ or by increasing thegas pressure required to achieve a desired increased flow. However, theeffectiveness of preheating flames has been found to be much less afunction of the volume of preheat gases delivered to the metalworkpiece, than the velocity and ratio of oxygen to fuel gas at whichthese preheat flames are delivered to the workpiece. Primarily, we havefound that by utilizing certain oxygen to fuel gas ratios, depending onthe particular fuel gas, and by delivering the preheat gas mixture atvelocities of about r 1000 feet per second, we can realize a muchreduced preheat period.

The preferred method of the invention comprises essentially the combineduse of highly oxidizing flames characterized by a high oxygen to fuelgas ratio delivered at supersonic gas velocities for preheating a metalsurface. The optimum ratio of oxygen-to-fuel gas, as mentioned above,varies from fuel gas to fuel gas and is that ratio which provides thehighest flame temperature. For example, tests have shown that the mosteffective natural gas preheat flames, as measured in terms of thepreheat time required to initiate the cutting reaction, are producedwhen the oxygen-to-natural gas ratio (by volume) is approximately 2to 1. This is graphically illustrated in FIG. 4. From this graph it willbe seen that for the same conditionsnamely, pierce starting on 2-in.plate with a preheat gas velocity of 1000 fps. and natural gas flow of65 c.f.l1., raising the oxygen-to-natural gas ratio from the almostuniversally used 1.7 to 1 to 2.0 to 1 results in a decrease in preheattime from 12 seconds to less than 5.5 seconds, or in effect, a decreaseof over 50 percent. Again referring to the curve, when the ratio ofoxygen-to-natural gas is increased beyond 2.1 to 1, the preheat timebegins to increase, primarily due to the effect of the excess oxygenwhich tends to cool the flame.

Similarly, as shown in the curve of FIG. 5, a reduction in preheat timeis realized when the ratio of oxygento-natural gas is held constant at 2to 1, and the exit-gas velocity of the preheat flames is increased. Wehave determined from the results of the tests, as indicated by thecurve, that there appears to be decreasing, if any, advantage gained byincreasing the gas velocity beyond 1600 f.p.s., and the largestpercentage of preheat time reduction is achieved at about 1000 feet persecond.

Forcomparison purposes, the .curve shown in FIG. 6, illustrates therelatively minor effect on the preheat time realized by merelyincreasing the volume of gas flow; this is contrasted to the combinedeffect of oxygen-tofuel gas ratio, and exit-gas velocity.

Though natural gas, due to its cost advantage, is the most widely usedfuel gas at the present time, propane and acetylene are also stillwidely used for many applications. Our tests have shown that anoxygen-to-propane ratio of about 5 to 1, as shown on the graph in FIG.7, produces the most elfective oxy-propane preheat flames. It has alsobeen determined in this respect that an oxygen-toacetylene ratio of 1.5to 1 produces the most effective oxyacetylene tiames. At theseprescribed ratios, the fiame temperatures are maximum.

In each instance, as noted above, about 1000 fps. has been determined asthe most practical exit-gas velocity since the most practical reductionin preheat time, occurs at approximately this velocity. Further, thereis the added advantage that this ve.ocity can be readily attainedutilizing the disclosed nozzle of the invention even with acetylene andthe low-pressure fuel gases maintained at supply pressures of about /2p.s.i. and less The increased rate of heat transfer realized by virtuethe preheat gases exiting from the flame ports at sup sonic velocity,and the resulting reduction in preheat time required to initiate thecutting reaction, are due in part to the more intimate contact of thehot gas molecules with the surface of the workpiece due to their highvelocity. This more intimate contact results in a scrubbing action alongthe work surface, which tends to more rapidly displace the cooler gasesfrom the surface.

The increased effectiveness of the oxidizing preheat flames, as measuredin terms of decreased preheat time, is not only the result of the higherflame temperature, due to the presence of the greater quantity ofoxygen, but also to a chemical combination of a portion of this oxygenwith the metal of the workpiece. It has been noted, for example, thatthe chemical oxidizing reaction takes place at the earliest possibletime after start of preheat and creates a rapid heat rise in the metal.Consequently, it is no longer necessary for a metal such as steel to bebrought up to a sweat temperature of about 1800" F. before rapidoxidation of the metal takes place. With the highratio, i.e., highoxygen-to-fuel gas ratio, preheat flames of the invention, it has beenfound that the actual cutting reaction takes place automatically at atemperature of about 1400", and furthermore, the process has t.- e addedadvantage of being clearly discernable by the operator. Therefore, evenan inexperienced operator wil lniow cxacty the instant that the cuttingoxygen should be turned on. Another even more important factor inpromoting this higher heat-transfer rate with the supersonic velocityhot gas molecules, is the greater mass concentration of heat per unitarea of work surface being heated.

The rapid preheat made possible by the use of preheating gas exitingfrom the flame ports at supersonic velocities and at high ratios ofoxygen-to-fuel gas according to the invention has resulted in preheattimes of five seconds or less for pierce starts on all ferrous metalthicknesses of /2 in. or over. For example, a pierce start was made inthe interior of a 2-in. thick ferrous metal plate using c.f.h. ofacetylene at an oxygen-toacetylene ratio of 1.5 to l and a velocity of1000 fps. in 1.1 seconds. A similar pierce start was made using c.f.h.of propane at an oxygen-to-propane ratio or" 5 to l and a velocity of1000 fps. in 3.4 seconds.

Referring again to FIG. 1, in order to obtain the desired supersonicpreheat gas velocity at the nozzle discharge, it has been found that thedischarge coefficient of any preheat gas outlet orifice is an importantfactor. The term discharge coefiicient, as we utilize it and as isgenerally accepted, refers to that characteristic of the nozzle asdetermined by the ratio of actual flow through the nozzle divided by thetheoretical flow, the maximum coefficient of course being 1.0. Forinstance, in conventional nozzles, it is not unusual to have gas portsin wln'ch the coefiicient of discharge is about 0.5 to 0.6, but in suchan instance, in order to achieve supersonic velocity discharge, it isnecessary to increa e the gas gage pressure to 20 or 30 psi. We havefound that with the presently disclosed preheat gas outlet in which thedischarge coeificient approaches 1.0, it is possible to obtain avelocity of 1000 fps. and upward with nozzle head pressures as low as 14psi. This is particularly advantageous when a low-pressure fuel gassupplied from a line at p.s.i. or less is used as the fuel source. Withthe advent of more efficient injectors in torch apparatus, it is nowpossible to aspirate the required low-pressure fuel gas flows into themixed gas stream in the torch apparatus, against a developed headpressure in the nozzle of 14 to 15 psi. Thus, the preheat flame portconfiguration of the invention, having a discharge coefficientapproximating 1.0 (0.90 or better), makes it possible to quite readilyachieve supersonic preheat gas discharge velocities when using thelow-pressure /2 p.s.i. or less) fuel gases.

Of course, generally speaking, critical velocity of any gas may beattained across the mouth of an orifice or port by adjusting the gaspressure such that the absolute pressure upstream of the mouth of theorifice is equal to or greater than 1.89 times the absolute pressuredownstream of the mouth of the orifice. This requires a minimum ofapproximately 13.5 psi. gage upstream of the mouth of the orifice whendischarging to the atmosphere. In the case of the conventionalcylindrical type or" preheat ports, for which the discharge coefiicientis between 0.5 and 0.6, th pressure drop through the cylindrical sectionof the port ahead of the mouth must be added to the 13.5 p.s.i.

mouth pressure to arrive at the total upstream pressure ahead of theorifice required to achieve the acoustic critical velocity of the gasacross the mouth of the orifice. In the instance of oxygen,the acousticcritical velocity is approximately 980 feet per second The continuationof the preheat port of the invention, which constitutes an essentialfeature, is the fact that the length of the metering inlet has been keptto an absolute minimum. This inlet, essentially a point as measured onthe longitudinal axis of the port, results in an orifice having adischarge coefficient approaching 1.0 (0.9 or better). Thus, thepressure drop through the orifice itself is virtually eliminated.Consequently, the pressure upstream of the orifice and the pressureupstream of the mouth of the orifice, are one and the same such that anupstream pressure of only 13.5 p.s.i. will produce critical velocityflow through the preheat ports of the invention.

As shown in FIGS. 1 and 2, the discharge end of the inner member 32 isprovided with a plurality of grooves 32 formed into the periphery ofsaid member to surround the central oxygen port Ed. The grooves extendrearwardly into annular passage 16 and are preferably tapered inwardlytoward the central axis of member 22 on the order of 1 to 3 as indicatedat angle a of FIG. 2 to provide for controlled lateral expansion ofexisting gas streams.

The peripheral grooves 32, as here Shown, may be formed with a roughlytriangular or V cross-section having a radius bottom; alternately,though, they may be formed with a flat or curved bottom such as alJ-shaped groove would provide. The grooves may be internally formed asshown on core 12 or may be externally formed on the inner wall of thejacket 14. It is essential in any event that the groove be so formed asto provide an expansion chamber having a configuration in which theflame port passage or chamber 39 defined by the groove and the surface40 of forward opening 23 on the jacket 14, is of particular proportions.For instance, in order to permit supersonic gas velocities to beachieved by the preheat gas stream as it emerges downstream of themetering inlet point 34 and into the flame port passage or expansionchamber 3%, the said passage 33 must gradually widen in crosssectionalarea such as provided by taper a", to permit controlled uniform lateralexpansion of the preheat gas stream. This controlled expansion providesfor a uniform velocity bu ldup exceeding the gas critical velocity. Sothe other hand, though, if the passage 3% is too divergent, the streamwill have a tendency to collapse due to over .in an excessively longport.

, plurality of spaced drillings.

increase in cross-sectional area 'to permit the desired con trolledexpansion of the preheat gas as it leaves the meter- ,ing port 34 so asto achieve uniform velocity buildup to supersonic velocity. A taper inexcess of 3 will, permit the passage to-widen too 'abruptlyand as aconsequence over expansion of the gas stream will result in a decreasedflow velocity. By' maintaining the outer passagewall 3i) relativelyparallel to the nozzle central axis, controlled expansion of the gasstream is substantially confined to a radially inward directon towardthe nozzle central axis. Thus, the preheat flames tend to convergetoward a point forward of the nozzle and thereby localize theconcentration of heat on the plate surface.

It has been found that not only does the cross-sectional area of theexpansion passage 3t constitute a vital factor in preheat gas velocity,but the length L of said passage as measured between the metering inletpoint 34 and the outer face 42 of core 12 is important. Best results interms of outlet velocity are obtained when the head pressure immediatelyupstream of metering point 34 is about 14 psi. and the ratio of passagelength L to the largest linear dimension at the metering inlet point 34is within the range of about 2 and 4 to 1. With this ratio, which maybereferred to as the aspect ratio, the /2 psi. pressure excessive oftherequired 13.5 p.s.i. to produce critical velocity, isravailable. Saidpressure, in combination with the controlled divergent port passagesection, serves to increase the velocity of gas discharging from theports, to a supersonic value (above critical velocity), rather than being utilized to overcome friction that would be present For example,referring to FIG. 3, if the height h of each groove, as measuredat themetering inlet point 34, is approximately of an inch, a proper length Lfor the flame passage 39 is within the range of about to ;-of an inch.

'It should be clearly understood at this point, that while we have shownthe preheat openings 30 as formed by grooves 32, the openings mayalternatively be formed by a In such'case, however, the relationship ofthe length L to the largest dimension across the passage 30 at themetering inlet point should be mainbination of features present in thenozzle, is one which 7 permits retention of the flame at the dischargeend in spite of supersonic exciting velocities. This is accomplished byproper positioning of the individual preheat ports with respect to eachother. The close, ring-like disposition, as shown in FIG. 3, permits theflame from one port to hold the flame of adjacent ports so that there isa mutually supporting beneficial action. Satisfactory flame reten tionisalso fostered by virtue of individual flame port divergency, aspreviously mentioned, a certain degree of taper or divergencyisessential to permit controlled lateral expansion of the gas stream,but it has been found that thefringe of each stream is suflicientlyretained to afiford a peripheral film which flows-at a velocity lessthan supersonic. This film, in effect, has a rate of discharge below therate of flame propagation for the particular preheat gas mixture.

Also, with respect to the gas mixture, because of the highoxygen-to-fuel gas ratio utilized, the rate of flame propagation isincreased and consequently the tendency f for the flame to blow off thenozzle is reduced.

In'achieving supersonic preheat velocities, we have found that the,disposition and nature of the metering inlet 34 is one of the most.pertinent factors of the invention. For example, and referring to FIGS.1v and 2, the metering inlet '34 is located in the chamber 15 .at thatpoint where the approach 'or shoulder 38 meets the forward. cylindricalopening .28. In that the grooves 32. are inwardly biased toward the coreaxis, the metering inlet constitutes the smallest cross-sectional areaof a flame port and is in effect a section with no actual. length atall. In reducing the critical metering inlet passage length toessentially a point, pressure loss, due to friction as the gas passesthrough the metering inlet passage, has been reduced to' virtually zero.Therefore, 13.5 p.s.i. pressure immediately upstream of the meteringinlet point 34 will result in critical velocity through the meteringinlet; Consequently, an available pressure of 14 psi,

' in combination with the relatively short narrow-angle For example, thepreheat passages of a single piece nozzle may constitute a plurality ofbores extending longitudinally through the nozzle and terminating at thedischarge face in flame ports as herein described. In such an instance,the flame parts may be fashioned having a circular cross-sectionalmetering inlet point and expansion chamber, by a reaming or swagingoperation. Hereto, the expansion passage is provided with the desiredpoint diameter.

One of the advantages of the method and apparatus.

of the inventionis that adjusting the gas ratio for the most effectivepreheat flames is a simple matter. Thus, even the most inexperiencedoperator is assured of achieving the mosteflective preheat withoutrecourse to flowmeters, or similar devices, in the gas supply lines. Toadjust the preheat flames to the proper ratio, it is merely necessarytostart with a flame on the fuel-rich side having' approximately thedesired volume of fuel gas. The oxygen supply is then graduallyincreased until the flame defining the inner cones are at their shortestlength and additional oxygen causes them to start to lengthen out again.The proper ratio of adjustment is at that point where the flames areshortest on the fuel-rich side. An improper setting of the preheat flamecones will fan out from the center line of the nozzle. On the otherhand, when properly adjusted, the flames fall in symmetricalalignmentaround the cutting jet and arewell formed, pointed cones.

In addition, it has been found that the location of the tip of the flamecones with respect to the surface of the workpiece is'an importantcontributing factor in achieving the most effective preheat. The optimumlocation, that is, when preheat time is at aminimum, occurs where theinner cones of the preheat flames just touch the surface of the platebeing heated. The flame cones impinging on the plate by as little as Ain. or off the surface as little as in. will rejsult in an increase inpreheat time of as much as 30 percent.

Practicing the method of the invention using the novel blowpipe nozzlenot only provides for greatly reduced preheat times of five seconds orless, for pierce starts in r the interior surface of a ferrous metalplate to be cut,

but also permit instantaneous edge starting, assuming that the startingedge is relatively sharp. This means that for ed e startin a relativel.sim le rocedure is followed in s s, y P P ano es? med for theparticular material thickness, adjust the flames as outlined above forcritical velocity and ratio, turn on the cutting oxygen, and start themachine travel to approach and traverse the workpiece. preheat andcutting reactions start simultaneously, vith no pause or hesitation asis normally required to initiate the cut.

A further advantage derived from the employment of such rapid heattransfer and pin pointconcentration of heat over a very short period,metal Warpage is substantially avoided. This is, of course, noteworthyfor thin or sheet metal cutting.

Another advantage residing in the use of supersonic gas velocity throughthe preheat port is the fact that generally for plate thicknesses inexcess of /2 in., thickness itself is not a factor effecting preheattime. In other words, the preheat time required to initiate the cuttingreaction is entirely independent of plate thickness and remains the somefor all thicknesses greater than /2 inch. In the instance of prior artlow-velocity, lovratio preheat, the preheat period is considerablylonger and therefore causes a wasteful dissipation of heat by conductionthrough the workpiece. Thus, with the prior art preheat method, platethickness is more of a contributing factor in the total preheat time inthat the thicker the plate the longer i takes to preheat it. Also, forcutting application, the big; -ratio supersonic velocity flames providethe shortest possible preheat time in order to initiate the cuttingreaction. Once the cut is started, the preheat flames may be cut back toprovide the desired soft flame to carry the cut and preserve good ourquality and provide a sharp top edge on the kerf.

it is understood that the method and apparatus herein disclosed anddescribed accomplished a decided improvement in the art ofthermochemical metal removing; it is ado apparent that modifications inthe unique method and nozzle may be made without departing from thespirit cope of the invention.

is a continuation-in-part of our application Serial 25,417, filed April28, 1960, and now abandoned.

What is claimed is:

1. Method for thermotreating a metal surface by directing thereonheating flames which comprises, providing a combustible gas mixture, atleast a portion of said mixture being a low-pressure fuel gas, formingsaid gas mixture into a stream under a head pressure up to about 15p.s.i.g., constricting said stream at a constricted metering inlethaving essentially no horizontal length to increase the velocity thereofto the critical velocity of said gas mixture, thereafter permittingcontrolled lateral expansion of said stream and directing said streamtoward the surface to be treated.

2. Method for thermotreating a metal surface by directing thereonheating flames which comprises, providing a combustible gas mixtureconsisting of a fuel gas chosen from the group consisting of acetylene,propane and natural gas together with a combustion supporting gas, foring said mixture into a stream under a head pressure up to about 15p.s.i.g., constricting said stream at a constricted metering inlethaving essentially no horizontal length to increase the velocity thereofto a value approximating the critical value of said gas mixture,controllably expanding said stream downstream of the constrictedmetering inlet to provide said stream with a velocity exceeding saidcritical velocity and directing the flames produced by the ignition ofsaid stream upon the surface to be treated.

3. In a nozzle having a discharge face for thermochernically treating ametal surface by directing thereon heating flames produced by an ignitedsupersonic velocity stream of a combustible gas mixture issuing from thenozzle discharge face, at least a portion of said gas mixture being agas supplied at low pressure, said nozzle comprising: an elongatedmember having a gas inlet end in opposed relation to the discharge face,a passage means ill communicating said inlet end with the discharge facefor directing a flow of the combustible gas mixture thereto, meansdefining an orifice at said face, means defining a throat rearward ofsaid discharge face, said throat adapted to receive a flow of gas fromthe passage, said throat having inwardly convergent Walls to direct saidgas flow to a metering inlet having essentially no horizontal lengthconstituting the smallest cross-sectional area of the throat, anexpansion chamber extending forward of said metering inlet and havingoutwardly divergent walls to provide an increasing cross-sectional areatoward the discharge face, said orifice characterized by a dischargecoeificient within the range of 0.9 to 1.0.

4. In a nozzle having a discharge face for thermochemically treating ametal surface by directing thereon heating flames produced by an ignitedsupersonic velocity stream of combustible gas issuing from the nozzledischarge face, at least a portion of said mixture being a gas suppliedat low pressure, said nozzle comprising: an elongated member having agas inlet end in opposed relation to the discharge face, and a chamberformed therein adjacent the discharge face, passage means communicatingsaid gas inlet with said chamber, means forming a plurality of orificescommunicating said discharge face with the said chamber, said orificesbeing circularly arranged to converge the gas streams issuing therefromat a point forward of said face, means defining a throat rearward ofsaid discharge face, said throat opening into said chamber, said throatdecreasing in cross-sectional area to a metering inlet constituting themost constricted portion of the throat, an expansion chamber commencingat said metering inlet and having outwardly divergent walls to providean increasing cross-sectional area toward the nozzle face, said orificecharacterized by a discharge coefficient within the range of 9.9 to 1.0.

5. In a cutting nozzle for thermo-chemically treating a metal surface bydirecting against said surface a preheating flame produced by an ignitedsupersonic velocity stream of a combustible gas mixture, a portion ofsaid mixture being a fuel gas supplied at low pressure, said nozzleincluding a gas inlet end and an opposed discharge face and comprising:an elongated jacket having an axial bore extending therethrough, a corecoaxially registered in said bore to define an annular passagetherebetween, passage means in said core communicating the gas inletwith the discharge face to conduct a flow of oxidizing gas, meansforming a plurality of orifices communicating the annular passage withthe discharge face, said orifices surrounding said passage means to forma plurality of circularly arranged outlets at the discharge face, eachof said orifices being formed with its axis inwardly directed toconverge the preheat flames issuing therefrom at a point forward of thedischarge face, means defining a throat rearward of said discharge face,said throat adapted to receive a flow of gas mixture from the annularpassage, said throat being formed by inwardly tapered walls to convergethe gas flow at a constricted metering inlet constituting the smallestcross-sectional area of the throat, an expansion chamber downstream ofsaid metering inlet to receive a high velocity constricted flow of gastherefrom, said expansion chamber having outwardly divergent walls toprovide an increasing cross-sectional area toward the discharge face,the length of said expansion chamber between the metering inlet anddischarge face being about 2 to 4 times the largest distance across saidmetering inlet, the length of said metering inlet being substantiallyWithout dimension.

6. In a cutting nozzle for thermo-chemically treating a metal surface bydirecting against said surface a preheating flame produced by an ignitedsupersonic velocity stream of a combustible gas mixture, a portionthereof being a fuel gas supplied at low pressure, said nozzlecomprising: an elongated outer jacket having at one end a gas inlet andat the other end a discharge face, said jacket having an axial boreextending therethrough, said rear'wardly adjacent the nozzle face, meansforming a passage extending through said core cornmunicatingthe gasinlet with the discharge'face to conduct a flow of oxidizing gas, thedischarge face of said core terminating in a recess from the extremeforward end of said jacket, the forwardportion of saidcore having adiameter slightly smaller than the jacket, cylindrical opening, saidcore forward portion being slideably received in said opening andclosely fitted therewith, a plurality of grooves formed into said coreforward portion extending to the face, thereof, said :gro-oves togetherwith the jacket forward Opening defining a plurality of orifices forconducting preheat; gas streams, each of said orifices being formed withits axis directed to converge the gas streams issuing therefrom at apoint forward of the nozzle face, means defining-a throat rearward ofsaid di schargeface, said throat having convergent walls to receive gasfrom the annular passage, and an expansion chamber having outwardlydivergent walls which terminate in a recessed outlet at the core face,said throat and expansion chamber being joined at the smallestcross-sectional area of each of said e E2 7 Y convergent anddivergentwalls respectively to define a metering inlet, the length ofsaid expansion chamber between the discharge face of the core and themetering inlet being from 2 to 4 times the largest distance across theopening at the metering inlet.

7. 'In a cutting nozzle substantially as described in claim 6 whereinthe core forward portion is provided with a plurality ,of adjacentlongitudinal grooves having a V shaped cross-section, said grooves beinginwardly tapered at an angle between 1 and 3 degrees, to define thedivergent Wall expansion chamber.

References Cited by the Examiner UNITED STATES PATENTS 2,531,00 11/50Smith 15s 27.4 2,861,900. 11/5 8 'Smith et a1. 158-274 2,993,531 7/61Spies et a1 1ss- 27.4 3,042,106 7/62 .Werner 1ss 27.4

I FOREIGN PATENTS 820,57 8/37 France.

JAMES W. ,WESTHAVER, Primary Examiner.

MEYER PERLIN, Examiner.

1. METHOD FOR THERMOTREATING A METAL SURFACE BY DIRECTING THEREONHEATING FLAMES WHICH COMPRISES, PROVIDING A COMBUSTIBLE GAS MIXTURE, ATLEAST A PORTION OF SAID MIXTURE BEING A LOW-PRESSURE FUEL GAS, FORMINGSAID GAS MIXTURE INTO A STREAM UNDER A HEAD PRESSUR UP TO ABOUT 15P.S.I.G., CONSTRICTING SAID STREAM AT A CONSTRICTED METERING INLETHAVING ESSENTIALLY NO HORIZONTAL LENGTH TO INCREASE THE VELOCITY THEREOFTO THE CRITICAL VELOCITY OF SAID GAS MIXTURE, THEREAFTER PERMITTINGCONTROLLED LATERAL EXPANSION OF SAID STREAM AND DIRECTING SAID STREAMTOWARD THE SURFACE TO BE TREATED.